Growth in demand for WLANs is driving the development of new technology to provide higher throughput. To a greater extent this growth is due to the increased number of users and applications desiring wireless transmission and to a lesser extent to the emergence of new applications needing higher transmission rates along a single connection between two points. Previous work has focused on increasing link throughput. This is necessary for single-stream high throughput applications. While it helps increase aggregate throughput, it is not the only way to do so. A MAC-based approach that enables the parallel use of multiple channels in a BSS, or a wireless mesh, can increase aggregate throughput. A mesh network is a network that employs one of two connection arrangements, full mesh topology or partial mesh topology. In the full mesh topology, each node is connected directly to each of the others. In the partial mesh topology, nodes are connected to only some, not all, of the other nodes. A mesh network may contain Mesh Points, Mesh Access Points (MAPs) and portals, collectively referred to as nodes. A portal is a gateway which provides an infrastructure mesh network access to a Distribution System (DS).
IEEE 802.11 has been allocated multiple non-overlapping channels. (i.e., three channels are available in the 2.4 GHz ISM RF band for 802.11b/g and twelve channels in the 5 GHz U-NII RF band for 802.11a). These channels can be used simultaneously, either in separate devices or in the same device. Ways to avoid the interference (referred to as adjacent channel interference or ACI) that would result from energy from the transmitter side lobes spreading out across the spectrum onto the other channel are described in co-pending provisional patent application titled “Mesh Mac and Adjacent Channel Interference”, application No. 60/709,820 filed Aug. 22, 2005. Multiple radios are useful in stations where high traffic concentration is expected.
An approach that offers both multi-channel and multi-radio capabilities appears in the co-pending patent application Ser. No. 11/393,127, titled “A Protocol For Wireless Multi-Channel Access Control”, filed Mar. 29, 2006, the disclosure of which is incorporated by reference herein. It describes the CCC (Common Control Channel) MAC protocol. CCC utilizes two types of logical channels, the control channel and the data channels.
The physical channel used by a node for control is static, it should not change rapidly. Therefore, for a node using a single radio, the choice of the physical channel to use for data traffic is fixed: it is the control channel. The physical channel(s) used by a node to transmit data traffic may be either fixed or vary dynamically. The different ways data channels may be assigned/selected range from totally fixed in advance to totally demand-based (i.e. dynamic).
When more than one radio is available at a node, the choice of a data channel may be totally or partially specified in advance. For nodes with multiple radios, three variants exist:
a) Fixed by source-destination node pair: The choice of data channel to transmit to a given neighbor node is fixed;
b) Fixed by source node: Of the channels assigned the source node, the choice of a channel to transmit varies; it is made at the time of transmission; or
c) Fixed by destination node: The source node selects from among data channel(s) assigned to the destination node
The source node must have advance knowledge of its neighbors' assigned data channels. In general, fixing the assigned channels at the source node generates a more compact re-use pattern and thus increases channel re-use efficiency